It may be obvious that, geopolitically speaking, a "vacuum zone" will inevitably be filled by outsiders. There is a not-so-funny joke that, if Japan's current demographic trend continues, there will be only one person left in the nation in 2200 — who will serve as the emperor, the prime minister and the president of Toyota Motor Corp. That may not be plausible indeed. But if the population decline in Japan continues at the current pace, "vacuum zones" will likely emerge across the nation that, at some point in the future, could lead to a large-scale inflow of people from outside the country.
Speaking as a native of Japan who was raised in this country — and is now traveling around the world and occasionally returning home — it's safe to say that people from abroad won't fail to notice if parts of this beautiful country are left vacant. Many of the good things about Japan that Japanese take for granted, such as its clean air, pure water, seasonal beauty and fertile soil are not commonplace overseas. A lot of people abroad live in places where they can't imagine enjoying those natural features.
These days, many of the inbound tourists to Japan are not satisfied with merely visiting Tokyo or Osaka but go on to travel to smaller cities in other regions of the country. In the first place, many people from overseas do not mind the inconveniences of living in natural environment in rural areas — they enjoy the "do it yourself " lifestyle and spend time engaging in farming in those areas. They do not complain that rural areas lack the convenience of urban life. What would these people think if they see houses left vacant and farmland deserted in increasing numbers? They would most likely feel excited.